This invention relates to apparatus for adjusting phases of cylinders for transferring sheets in a sheet-fed rotary printing press provided with a sheet turn-over mechanism for printing both sides of the sheet.
In recent years, there has been developed a sheet-fed rotary printing press provided with a turn-over mechanism so that it can print one side or both sides of a sheet. FIGS. 1 and 2 are side views of the printing press near its turn-over cylinder and are useful to explain the sheet transfer operation of the printing press of this type at the time of printing one side and at the time of printing both sides of the sheet. FIG. 1 shows one side printing, while FIG. 2 both side printing. More particularly, a turn-over cylinder 2 is provided on the downstream side of an impression cylinder 1 of a first printing unit, and an impression cylinder 3 of a second printing unit is provided on the downstream side of the turn-over cylinder 2. A sheet 5 printed between the impression cylinder 1 and a blanket cylinder 4 of the first printing unit is sent between the impression cylinder 3 and a blanket cylinder 6 of the second printing unit via the turn-over cylinder 2 by the operation of gripper-to-gripper transfer, so as to be subsequently printed. Comparing one side printing with both side printing, in the one side printing shown in FIG. 1, the sheet 5 with its front surface 5a printed is released from grippers 7 of the impression cylinder 1 and then gripped by tumbler grippers 8. After the turn-over cylinder 2 has rotated about 180.degree., the sheet 5 is gripped by grippers 9 of the impression cylinder 3 to be subjected to the next printing. At this time, since the sheet wrapped about the impression cylinder 3 has its front surface 5a faced outward, one side printing is performed. On the other hand, in the case of the both side printing shown in FIG. 2, the upper surface 5a of the sheet 5 is printed while it passes between the impression cylinder 1 and the blanket cylinder 4 and the sheet 5 passes through a contact point between the turn-over cylinder 2 and the impression cylinder 1 while being gripped by grippers 7 so that the sheet 5 is wrapped about the impression cylinder 1. As the trailing end of the sheet 5 reaches the contact point between both impression cylinder 1 and turn-over cylinder 2, the trailing end is gripped by the tumbler grippers 8. At this time, the grippers 7 are opened to release the sheet 5 so that as the turn-over cylinder 2 rotates, the sheet 5 will be brought to the impression cylinder 3 under a reversed state and wrapped about the impression cylinder 3 with its upper surface 5a in contact with the impression cylinder 3 by the operation of the grippers, whereby its rear surface 5b is printed. In this case, different from the one side printing, the tumbler grippers 8 are advanced from the side of the trailing end of the sheet 5 to grip the sheet 5. After rotating with the turn-over cylinder 2, the grippers 8 release the sheet 5. Accordingly, cams for operating the grippers are provided with cam surfaces such that the tumbler grippers 8 rotate substantially 180.degree. during one revolution.
With the printing press provided with such turn-over mechanism, as can be clearly understood by comparing FIGS. 1 and 2, grippers 7 and tumbler grippers 8 which oppose each other in FIG. 1, but in FIG. 2, grippers 7 and 8 are dephased by a wrap angle .theta. of the sheet 5, and by an angle .alpha. of the rotation of the tumbler grippers 8. Accordingly, when switching from the one side printing to the both side printing or vice versa, it is necessary to make different the phase of a group of cylinders, including the turn-over cylinder 2 and the following cylinders from the phase of a group of cylinders including the impression cylinder 1 and the following cylinders by an angle .theta. corresponding to the size of the sheet 5 and by an angle .alpha. of the rotation of the tumbler grippers 8. Further, it is also necessary to adjust the phases when the size of the sheet 5 varies during both side printing.
As the phase adjusting apparatus, the following apparatus have been generally used. More particularly, two adjacent gears meshing with a gear of the impression cylinder 1 are provided for the turn-over cylinder 2, one being fixed to the shaft of the turn-over cylinder 2 and the other being rotatably mounted on the shaft. During operation, the two gears are fixed together to transmit the rotation of the impression cylinder 1 to the turn-over cylinder 2, whereas for adjusting the phase, the two gears are separated, the rotatably mounted gear is rotated together with the group of cylinders including the impression cylinder 1 to position them, and thereafter the two gears are fixed together to transmit the rotation.
With the prior art phase adjusting apparatus, however, the two gears are fixed with 4 to 6 bolts and a clamping plate so that at each phase adjustment the bolts are loosened or tightened for separating or fixing the gears. This not only requires much time but also a large space for the adjustment.